Repeater for pulse communication system



Dec. 28, 1948. e. H. HUBER REPEATER FOR PULSE COMMUNICATION SYSTEM Filed Feb. 15, 1945 RAD/O P-MULTIPLE E REC. 25c.

KY F /,2 /3

as male TRANS /0 TRANS INVENTOR By a H. HUBER ATTORNEY- .munication.

Patented Dec. 28, 1948 UNITED STATES OFFICE .REPEATER FOR PULSE .JCOMMUNICATION SYSTEM :George .Huber, 1Manhasset, .N. Y., assignor to Bell Telephone Laboratories, Incorporated, New .York, N. Y., a corporation of New .York

Application February 15, 1945, Serial No. 577,954

1 Claim. -1

This invention relates to repeaters and particularly to repeaters for pulsed-type communication systems and more particularly to multiplex systems of that type.

An object of the invention is the correction of pulse distortion.

In electrical communication systems in which transmission is carried out by means of modulated pulses the conditions of transmission and the effects of terminal equipment may be such as to materially distort the shape of the pulses.

lating pulses. In a usual type of radio :repeater the received signals are brought down to the pulse frequency level where they are amplified and used to modulate a radio frequency transmitting oscillator in the same way as at the terminal. As a result the same pulse shortening effect is produced and the effect is cumulative. Where several repeaters are used in tandem the total effect may cause such a deterioration of the pulses as to seriously interfere with com- Such effects are particularly noticeable in systems utilizing short pulses and operating at very high frequencies where direct amplification is difficult.

A particular object of the [invention is to re- ;store the length of pulses shortened by the effects of translation or transmission.

In multiplex systems where adjacent pulses carry the modulationsof different channels it .is necessary that the system used for lengthening the pulses shall not produce such trailing edges on the reformed pulses as will extend over into the frame period assigned to an adjacent pulse. Such methods of pulse reshaping introduce crosstalk between channels which may be sufiiciently great to be objectionable. A further object of the invention is to lengthen the pulses of a multiplex system without introducing cross-talk between channels.

In accordance with a feature of this invention the repeater includes a delay network for producing a second pulse following each input pulse to the repeater by a time equal to the desired increase in length for the repeated pulses which should not be greater than length of the input pulse. The combination of each trans- .no delay. .However, the preferable arrangement is .to connect across the repeater one set of terminals :of a .delay network that is open-:circuited .at the other set of terminals. As a result, the effect :of aapulsejn the repeater is to produce a second pulse reflected-from the open-circuited end of the {delay network and consequently following 'therfirst pulse at a time equal to twice the delay time :of the network.

These and other objects, features and aspects of the invention may be better understood by reference to the following detailed description in :connection withthe drawing in which:

Fig. 1 is a block schematic showing of repeated pulsed radio telephone systems in accordance .with the invention;

Fig. 2.-is a detailed block-schematic diagram of the repeater of Fig. 1;

:Fig. 3 is adetailed block schematic of a modified form of -the repeater 9, Fig. 1; and

Figs. 4, 5 and 6 are explanatory diagrams of the operation of 'the repeater.

vFig..1:shows a one-way multiplex pulse modulation radio system comprising a transmitting terminal-I 'a radio repeater =2 and a receiving ter- -minal 3. As indicated by the spacing and dotted dine between the radio repeater 2 and the receiv- :ing terminal .3, other radio repeaters may be included in the systemas required by distance separating the terminals and the nature of the in- -.tervening country.

The transmitting terminal I comprises a multiplex transmitter :5 .of any of the known types of time divisionpulse modulation, for example, a pulse position modulation system as shown in the copending application of J. O. Edson, Serial No. 559,354, filed October 19, 1944. The output of the multiplex transmitter is applied to the radio transmitter 6 which is keyed to produce pulses of ultra-high frequency radio oscillations by the pulse output of the multiplex transmitter. These radio waves are transmitted from a directional antenna 1.

The waves from the antenna 1 are received at the repeating station 2 in an antenna 8, de-

tected in the radio receiver 9 and the resultant direct current pulses supplied to the repeater In Where they are amplified and reshaped and supplied to a radio transmitter H similar to the transmitter 6. The resultant pulses of radio pulse. is connected to the input of a final amplifier 23.

f3 waves from the transmitter II are radiated b the directional antenna l2.

At the receiving terminal 3 the waves from the antenna l2 or a similar antenna of a subsequent repeater are received in the antenna I3, detected in the radio receiver [4 and the resultant pulses supplied to the receiving multiplex l5 which may be of the type disclosed in the Edson application identified above.

Fig. 2 shows one form of the repeater II]. This comprises an amplifier 2i the outputof which is coupled to the input of a limiting amplifier.

or clipper 22. Connected across the connections between the amplifiers 2| and. 22 is one set of terminals of the delay network 26 which is desiged to match the impedance of the connecting circuit. The delay network 26 is open-circuited at its other terminal. It is necessary that the upper frequency at which the network 26 operates be sufficiently high that the edge of the reflected pulse does not trail off so as to extend into the period assigned to an adjacent The output of the limiting amplifier 22 The operation of the repeater II) can be best understood by reference to the diagrams of Figs. 4, 5 and 6 in each of which voltage is plotted against time to show the wave form of variou components in the system.

Fig. 4 shows the output of the amplifier 2| comprising the marker or synchronizing pulse 24 and two of the channel pulses 25. In Fig. 5

the output of the delay network 26 is shown. This comprises the delayed marker pulse 24A and the delayed channel pulses 25A. All of these pulses are delayed with respect to the exciting pulses of Fig. 4 by-a time 2d equal to twice the delay (d) of the network 26. The input to the clipper or limiting amplifier 22 is shown in Fig. 6.

This comprises the sum of the pulses of Figs. 4

and 5 as may be seen by observation. The efiect of the clipper 22 isto transmit only those amplitudes below the limiting value represented by the dotted line 28. This results in an output from the clipper 22 represented by the lower portion of the pulses 24B and 253. These will be observed to be pulses of the same general typeas the original pulses 24 and 25'but each lengthened by an amount 2d. The increase of length of each pulse is the same and independent of the relative lengths of the original pulses. By proper design of the delay network, the increase may be made to substantially compensate the shortening that takes place in the transmitting oscillator.

These reformed or lengthened pulses 22A and 253 after being subjected to the clipping action of the amplifier 22 are amplified in the subse- 4 quired for keying the transmitter l l in the same way that the terminal transmitter 6 is keyed.

Fig. 3 shows. a modified form of the circuit of the repeater Hi. In this circuit the output of the radio receiver 9 is branched to two amplifiers 3i and 32. The output of amplifier 3! is supplied directly to the input of the limiting amplifier 34. The output of the amplifier 32 is supplied through the delay network 33 to the amplifier 34. In this case, as in that of Fig. 2, the input to the amplifier 34 will be the sum of two sets of pulses one directly through the amplifier 3| and the other delayed by the network 33. In this case the amount of delay produced will be exactly equal to the delay time of the network 33 since the transmission therethrough is in only one direction. Accordingly, in order to obtain the same length correction the network 33 must have twice the delay of the network 26. The clipping action of the limiting amplifier 3'4 and the subsequent amplification by the amplifier 35 ,is the same as bythe corresponding amplifiers 22 and 23 of Fig. 2.

What is claimed is:

In a system for communication by modulated pulses of high frequency waves at least one repeater including a receivenfor detecting the incoming high frequency waves, an amplifier for the pulse output of said receiver, a transmitter for generating new pulses of high frequency waves in response to the pulse output of said amplifier and operating inherently to produce pulses of high frequency waves of shorter duration than the signal pulse'input from said am plifier, and a pulse shaping-circuit associated with said amplifier and comprising an openended delay network having its input terminals connected to the amplifier path and of such characteristics as to reflect each pulse at said ter- REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,200,009 'Nuttall May 7, 1940 2,211,942 White Aug. 20, 1940 2,254,204 Blumlein Sept. 2, 1941 2,262,838 Deloraine et al. Nov. 18, 1941 2,415,359 Loughlin Feb. 4, 1947 

